LB 8-65 - Predicting ozone effects on growth of large aspen trees from seedling response functions developed from field chambers.

Tropospheric ozone is one of the most pervasive and harmful air pollutants known to affect natural and agricultural ecosystems in the United States. In the U.S., the Environmental Protection Agency (USEPA) and other Agencies are concerned with protecting plants and ecosystems from harmful ozone exposures. Controlled exposure experiments conducted in field chambers have been used to establish tree growth response relationships to ozone exposure for more than 16 species. However, these experiments were limited to small trees seedlings. One major question from these studies is whether the exposure-response relationships from seedlings are applicable to larger trees growing in a more realistic environment. We used the ozone exposure response relationships developed in several field chamber studies on trembling aspen (Populus tremuloides) seedlings to predict the growth results on the same species grown in the Aspen-FACE “free-air” ozone exposure experiment over 11 years. To do this we acquired the individual tree growth data and hourly ozone exposure from the ambient and elevated ozone plots from the Aspen-FACE experiment in Rhinelander, WI. We were able to create comparable ozone exposure and growth metrics for each of the study types. Over the 11 years of the Aspen-FACE experiment, we very closely predict the percent above-ground biomass loss due to ozone using simple empirical models derived from the chamber studies. The effect of ozone exposure established in early years of the Aspen-FACE experiment continued to be observed throughout later years. In conclusion, our study suggests that ozone exposure response relationships developed in chambers on seedlings are very relevant for making inferences about effects on larger trees. These results imply that researchers can use these relationships with more confidence when estimating risks to ozone pollution across the U.S. The views expressed in this abstract are those of the author(s) and do not necessarily represent the views or the policies of the U.S. Environmental Protection Agency.